1. Field of the Invention
This invention relates to means for adjusting the caster angle of the steerable wheels of motor vehicles.
2. Description of Related Art
Automotive designers have incorporated various means for adjusting the suspension parameters caster, camber, and toe. The present invention is concerned with the adjustment of caster on monobeam, twin-I-beam or other front axles. Caster angle is the angle included between a vertical plane passing through the wheel spindle and a line passing through and concentric with the longitudinal center line of the kingpin. Caster angle is measured in a vertical plane running parallel to the longitudinal center line of the vehicle.
Caster and camber adjustments may be performed by means of similar mechanisms with some automotive suspensions and several different types of devices have been used to adjust one or both of these parameters. U.S. Pat. No. 4,213,631 discloses an indexable plate for independently or simultaneously changing the caster and camber angles of the front wheels of a vehicle having a single axis suspension device such a a McPherson strut. Some suspensions have incorporated adjustable links for the purpose of changing caster or camber. Examples of these are disclosed in U.S. Pat. No. 2,115,915 which illustrates the use of turnbuckles and U.S. Pat. No. 3,819,202, which incorporates an adjustable strut between the wheel carrier and a vehicle cross member. Various systems have been used for changing caster and camber through adjustment of slotted devices. U.S. Pat. Nos. 2,065,071, 2,122,961, 3,285,622, 4,011,626, 4,418,938, and 4,420,170 all disclose means of this type. Ford Motor Company's 1984 model truck shop manual for light trucks at pages 19-01-2 and 19-01-9 discloses a method for adjusting caster angle using only the available clearances provided by the mounting holes for a fastener which connects the axle to the radius arm. A similar method involves manually slotting a mounting hole in a radius arm to achieve an equivalent result.
Devices incorporating cams have also proven useful for adjusting automotive suspensions. Examples of such devices are disclosed in U.S. Pat. Nos. 2,556,767, 2,890,893 and 3,880,444.
Caster angle is important in vehicle suspensions because it is the caster adjustment which provides part of the tendency of the vehicle's wheels to return to a straight ahead position following negotiation of a curve. A side-to-side difference in caster angle can cause the vehicle to drift or pull in one direction. The indexable caster adjusting plate of the present invention is useful for correcting this side-to-side variation in caster angle.